Sifting fact from fiction

Looking for clues ... Scientist and author Jennifer Marohasy: ‘‘It’s a myth that the Murray’s mouth was ever deep and wide.’’

1 of 3

Dredges working to keep the Murray mouth clear where the Coorong meets the sea.

2 of 3

The Murray mouth from the air.

3 of 3

5370537724001

South Australia can make a good argument about the preservation of the ecosystem around the Lower Lakes and the Coorong.

The lower end of the Murray River empties into two large lakes, Alexandrina and Albert, which then flow into the area known as the Coorong, a strip of national park running south-east of Goolwa.

The South Australian Government has built weirs, known as barrages, to prevent an inflow of salinised seawater into the lakes and the Murray River and to maintain lake levels.

The main species of fish affected by low lake levels and salinised water are small-bodied fish such as Yarra pygmy perch, Murray hardyhead, southern pygmy perch and the southern purple spotted gudgeon.

These species are endemic to the wetlands that fringe Lake Alexandrina and some of the wetlands along the Murray River channel.

With the exception of Murray hardyhead, which can survive in brackish water, the other three fish species require fresh water to support their preferred habitat type and for physiological requirements.

Other key biota in the Lower Lakes affected by low water levels and salinised water are frogs; large-bodied fish, such as golden perch; cryptic waterbirds, such as bitterns, crakes and rails; and populations of colonial breeding waterbirds, such as cormorants, spoonbills and ibis.

South Australia Department for Environment and Water spokesperson Jarrod Eaton, who is the River Murray water operations manager, said if water levels in the Lower Lakes were low, fresh water could not be delivered to the Coorong via the barrages.

‘‘As evidenced during the millennium drought, a salinised Coorong cannot support EPBC-listed migratory waders, other EPBC-listed waterbirds such as fairy terns and hooded plovers, and estuarine and diadromous fish,’’ Mr Eaton said.

Riverina farmer and Murray-Darling Basin researcher Louise Burge said historical records showed during major periods of drought, the Murray and Darling rivers would have dried completely or to a series of pools.

Under these scenarios, end-of-river-system flows could be zero or negligible, if assessed as flows from the Murray River itself.

The Murray River system and its relationship with the Southern Ocean, is not dissimilar to many other Australian tidal inlet systems.

A narrow opening to the sea, the continual sand deposits that occur with incoming tides and the site’s interaction with natural coastal climatic events, such as storm surges, are a major feature of tidal inlet systems.

As evidence of the huge task required to keep the mouth open, Ms Burge points to the last Murray River flood in 2016.

While the resulting high flows opened the mouth for a while, she said within a week, the dredges were required again.

Scientist Jennifer Marohasy has discovered that the Murray’s mouth was blocked by sandbars when explorer Charles Sturt sailed down the river in 1830.

‘‘Since European settlement there have been many attempts to widen and deepen the Murray River’s sea mouth to make it more permanently navigable, including through blasting and dredging,’’ Dr Marohasy said.

‘‘More recently, a national consensus has formed around the idea that if there were less irrigation upstream, the Murray’s mouth could be restored to its former glory.

‘‘But it’s a myth that the Murray’s mouth was ever deep and wide.’’

Retiring NSW senator David Leyonhjelm has said some South Australians were in denial about the cause of the declining Coorong, ‘‘which is the diversion of fresh water away from the Coorong and out to sea via the South East Drainage Scheme’’.

‘‘Rather than return South Australian water to the Coorong, they want to use water from Victoria and NSW to try to save it.’’

Here is the rub for Victorian and NSW irrigators.

The Murray-Darling Basin Plan agreement was for the delivery of 2750Gl of environmental water, but there was a further 450Gl added later.

The extra 450Gl carries the condition that there would be neutral or positive socio-economic impacts from recovering this water.

The qualification is frequently ignored, as the South Australian Government has told Country News: ‘‘The final 450Gl detailed in the basin plan must be recovered to ensure a healthy Lower Lakes and Coorong, as well as the enhanced environmental outcomes listed in Schedule 5 of the basin plan’’.

South Australians may well argue they are putting the environment ahead of commercial or farming considerations, but that would not be the whole story.

The Coorong and Lower Lakes have been recognised under the Ramsar convention on wetlands, but there are also commercial considerations for the region, with more than 30 licensed commercial fishing operations, about 600 licensed water users, including irrigators, drawing water from the lakes and lifestyle holiday housing being built around the lakes.

Waterfront houses on Hindmarsh Island and its marinas sell for between $500000 and more than $1million.